Payload points count on HUD

To save time and trial and error, how many CP's does the single stage Payload HUD support? I know Badwater has 4 visible and i remember that there could have been maps that have even 5 but will the map work without problems and without any gimmics?

That's not entirely correct, the same 8 CP limit counts for A/D cp and (5)cp push maps too. It's not the train controller which has that limit and even if it was, that's only semantics. The point is, TF2 can only handle 8CP's in any one map (whether it's payload, attack defend or control point push).